Based on the principle of information theory, a novel scheme of unequal-interval frequency-hopping (FH) systems was proposed. For cases of spectrum overlapping systems and non-overlapping systems, the implementation m...Based on the principle of information theory, a novel scheme of unequal-interval frequency-hopping (FH) systems was proposed. For cases of spectrum overlapping systems and non-overlapping systems, the implementation methods were presented and the security performances were discussed theoretically. Firstly, the definitions of absolute and relative key amounts of FH systems, equal-interval and unequal-interval FH systems were given. Then, the absolute key amount and relative key amount were analyzed for equal-interval and unequal-interval FH systems. The results indicated that the absolute key amount had become the key point in improving the security and secrecy of FH systems, especially in today's epoch of highly developed computer science and IC design technology. Theoretical analysis and practical examples showed that the absolute key amount of unequal-interval FH systems was generally over two orders larger than that of equal-interval ones when spectrum overlapping was allowable. Therefore, there was great superiority in enhancing the security and secrecy for the scheme mentioned.展开更多
BeiDou regional navigation satellite system （BDS） also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit （GEO）, 5 satel...BeiDou regional navigation satellite system （BDS） also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit （GEO）, 5 satellites in Inclined Geosynchronous Orbit （IGSO）, and 4 satellites in Medium Earth Orbit （MEO）. In this paper, its basic navigation and positioning performance are evaluated preliminarily by the real data collected in Beijing, including satellite visibility, Position Dilution of Precision （PDOP） value, the precision of code and carrier phase measurements, the accuracy of single point positioning and differential position- ing and ambiguity resolution （AR） performance, which are also compared with those of GPS. It is shown that the precision of BDS code and carrier phase measurements are about 33 cm and 2 mm, respectively, which are comparable to those of GPS, and the accuracy of BDS single point positioning has satisfied the design requirement. The real-time kinematic positioning is also feasible by BDS alolae in the opening condition, since its fixed rate and reliability of single-epoch dual-frequency AR is comparable to those of GPS. The accuracy of BDS carrier phase differential positioning is better than 1 cm for a very short baseline of 4.2 m and 3 cm for a short baseline of 8.2 km, which is on the same level with that of GPS. For the combined BDS and GPS, the fixed rate and reliability of single-epoch AR and the positioning accuracy are improved significantly. The accu- racy of BDS/GPS carrier phase differential positioning is about 35 and 20 % better than that of GPS for two short baseline tests in this study. The accuracy of BDS code differential positioning is better than 2.5 m. However it is worse than that of GPS, which may result from large code multipath errors of BDS GEO satellite measurements.展开更多
The truncation error and propagation error are analyzed for velocity determination through differential GPS carrier phase observations,and an approach for the choice of the best number of points for the central differ...The truncation error and propagation error are analyzed for velocity determination through differential GPS carrier phase observations,and an approach for the choice of the best number of points for the central difference method is developed.In order to overcome the disadvantages of existing GPS velocity determination methods,a new velocity determination algorithm is presented,based on combining carrier phase and Doppler observations.The basic idea is that two types of observation are combined by adding their normal equations,and their weights are evaluated by strict Helmet variance-components estimation.In order to control the influence of outliers,a bifactor equivalent weights strategy is adopted.To validate this method,GPS data of the airborne gravimetry campaign MEXAGE2001 is tested.The results show that the precision and reliability of velocity determination are obviously improved by using the proposed method.展开更多
文摘Based on the principle of information theory, a novel scheme of unequal-interval frequency-hopping (FH) systems was proposed. For cases of spectrum overlapping systems and non-overlapping systems, the implementation methods were presented and the security performances were discussed theoretically. Firstly, the definitions of absolute and relative key amounts of FH systems, equal-interval and unequal-interval FH systems were given. Then, the absolute key amount and relative key amount were analyzed for equal-interval and unequal-interval FH systems. The results indicated that the absolute key amount had become the key point in improving the security and secrecy of FH systems, especially in today's epoch of highly developed computer science and IC design technology. Theoretical analysis and practical examples showed that the absolute key amount of unequal-interval FH systems was generally over two orders larger than that of equal-interval ones when spectrum overlapping was allowable. Therefore, there was great superiority in enhancing the security and secrecy for the scheme mentioned.
基金sponsored by the National Natural Science Foundation of China(Grant Nos.41020144004,41374019,41104022)the National High Technology Research and Development Program of China(Grant No.2013AA122501)
文摘BeiDou regional navigation satellite system （BDS） also called BeiDou-2 has been in full operation since December 27, 2012. It consists of 14 satellites, including 5 satellites in Geostationary Orbit （GEO）, 5 satellites in Inclined Geosynchronous Orbit （IGSO）, and 4 satellites in Medium Earth Orbit （MEO）. In this paper, its basic navigation and positioning performance are evaluated preliminarily by the real data collected in Beijing, including satellite visibility, Position Dilution of Precision （PDOP） value, the precision of code and carrier phase measurements, the accuracy of single point positioning and differential position- ing and ambiguity resolution （AR） performance, which are also compared with those of GPS. It is shown that the precision of BDS code and carrier phase measurements are about 33 cm and 2 mm, respectively, which are comparable to those of GPS, and the accuracy of BDS single point positioning has satisfied the design requirement. The real-time kinematic positioning is also feasible by BDS alolae in the opening condition, since its fixed rate and reliability of single-epoch dual-frequency AR is comparable to those of GPS. The accuracy of BDS carrier phase differential positioning is better than 1 cm for a very short baseline of 4.2 m and 3 cm for a short baseline of 8.2 km, which is on the same level with that of GPS. For the combined BDS and GPS, the fixed rate and reliability of single-epoch AR and the positioning accuracy are improved significantly. The accu- racy of BDS/GPS carrier phase differential positioning is about 35 and 20 % better than that of GPS for two short baseline tests in this study. The accuracy of BDS code differential positioning is better than 2.5 m. However it is worse than that of GPS, which may result from large code multipath errors of BDS GEO satellite measurements.
基金supported by the National High Technology Research and Development of China (Grant No.2006AA12Z22)the National Natural Science Foundation of China (Grant No.40604003)+1 种基金the Foundation for Author of National Excellent Doctoral Dissertation of China (Grant No.2007B51)the China Postdoctoral Science Foundation (Grant No.20080430148,2009020444)
文摘The truncation error and propagation error are analyzed for velocity determination through differential GPS carrier phase observations,and an approach for the choice of the best number of points for the central difference method is developed.In order to overcome the disadvantages of existing GPS velocity determination methods,a new velocity determination algorithm is presented,based on combining carrier phase and Doppler observations.The basic idea is that two types of observation are combined by adding their normal equations,and their weights are evaluated by strict Helmet variance-components estimation.In order to control the influence of outliers,a bifactor equivalent weights strategy is adopted.To validate this method,GPS data of the airborne gravimetry campaign MEXAGE2001 is tested.The results show that the precision and reliability of velocity determination are obviously improved by using the proposed method.
